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<span id="more"></span>

<p><strong>位图使用步骤：</strong></p>
<p>1.创建Image的子类对象BufferedImage(int width,int height,int ImageType),创建时需要指定位图的宽高及类型属性；此时相当于在内存中生成了一张图片；</p>
<p>2.调用BufferedImage对象的getGraphics()方法获取画笔，此时就可以往内存中的这张图片上绘图了，绘图的方法和之前学习的一模一样；</p>
<p>3.调用组件的drawImage()方法，一次性的内存中的图片BufferedImage绘制到特定的组件上。</p>
<p><strong>使用位图绘制组件的好处：</strong></p>
<p>使用位图来绘制组件，相当于实现了图的缓冲区，此时绘图时没有直接把图形绘制到组件上，而是先绘制到内存中的BufferedImage上，等全部绘制完毕，再一次性的图像显示到组件上即可，这样用户的体验会好一些。</p>
<p><strong>案例：</strong></p>
<p>​    通过BufferedImage实现一个简单的手绘程序：通过鼠标可以在窗口中画图。   </p>
<center>
<img src="https://pic.imgdb.cn/item/62561f9c239250f7c58a0ce8.jpg">
</center>

<p><strong>演示代码：</strong></p>
<figure class="highlight java"><div class="table-container"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span 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class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br></pre></td><td class="code"><pre><code class="hljs java"><span class="hljs-keyword">import</span> java.awt.*;<br><span class="hljs-keyword">import</span> java.awt.event.*;<br><span class="hljs-keyword">import</span> java.awt.image.BufferedImage;<br><br><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">HandDraw</span> </span>&#123;<br>    <span class="hljs-comment">//定义画图区的宽高</span><br>    <span class="hljs-keyword">private</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> AREA_WIDTH = <span class="hljs-number">500</span>;<br>    <span class="hljs-keyword">private</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> AREA_HEIGHT = <span class="hljs-number">400</span>;<br>    <span class="hljs-comment">//定义变量，保存上一次鼠标拖动时，鼠标的坐标</span><br>    <span class="hljs-keyword">private</span> <span class="hljs-keyword">int</span> preX = -<span class="hljs-number">1</span>;<br>    <span class="hljs-keyword">private</span> <span class="hljs-keyword">int</span> preY = -<span class="hljs-number">1</span>;<br>    <span class="hljs-comment">//定义一个右键菜单，用于设置画笔的颜色</span><br>    <span class="hljs-keyword">private</span> PopupMenu colorMenu = <span class="hljs-keyword">new</span> PopupMenu();<br>    <span class="hljs-keyword">private</span> MenuItem redItem = <span class="hljs-keyword">new</span> MenuItem(<span class="hljs-string">&quot;红色&quot;</span>);<br>    <span class="hljs-keyword">private</span> MenuItem greenItem = <span class="hljs-keyword">new</span> MenuItem(<span class="hljs-string">&quot;绿色&quot;</span>);<br>    <span class="hljs-keyword">private</span> MenuItem blueItem = <span class="hljs-keyword">new</span> MenuItem(<span class="hljs-string">&quot;蓝色&quot;</span>);<br>    <span class="hljs-comment">//定义一个BufferedImage对象</span><br>    <span class="hljs-keyword">private</span> BufferedImage image = <span class="hljs-keyword">new</span> BufferedImage(AREA_WIDTH,AREA_HEIGHT,BufferedImage.TYPE_INT_RGB);<br>    <span class="hljs-comment">//获取BufferedImage对象关联的画笔</span><br>    <span class="hljs-keyword">private</span> Graphics g = image.getGraphics();<br>    <span class="hljs-comment">//定义窗口对象</span><br>    <span class="hljs-keyword">private</span> Frame frame = <span class="hljs-keyword">new</span> Frame(<span class="hljs-string">&quot;简单手绘程序&quot;</span>);<br>    <span class="hljs-comment">//定义画布对象</span><br>    <span class="hljs-keyword">private</span> Canvas drawArea =  <span class="hljs-keyword">new</span> Canvas()&#123;<br>        <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">paint</span><span class="hljs-params">(Graphics g)</span> </span>&#123;<br>            <span class="hljs-comment">//把位图image绘制到0,0坐标点</span><br>            g.drawImage(image,<span class="hljs-number">0</span>,<span class="hljs-number">0</span>,<span class="hljs-keyword">null</span>);<br>        &#125;<br>    &#125;;<br>    <span class="hljs-comment">//定义一个Color对象，用来保存用户设置的画笔颜色,默认为黑色</span><br>    <span class="hljs-keyword">private</span> Color forceColor = Color.BLACK;<br>    <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">init</span><span class="hljs-params">()</span></span>&#123;<br>        <span class="hljs-comment">//定义颜色菜单项单击监听器</span><br>        ActionListener menuListener = <span class="hljs-keyword">new</span> ActionListener() &#123;<br>            <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">actionPerformed</span><span class="hljs-params">(ActionEvent e)</span> </span>&#123;<br>                String command = e.getActionCommand();<br>                <span class="hljs-keyword">switch</span> (command)&#123;<br>                    <span class="hljs-keyword">case</span> <span class="hljs-string">&quot;红色&quot;</span>:<br>                        forceColor=Color.RED;<br>                        <span class="hljs-keyword">break</span>;<br>                    <span class="hljs-keyword">case</span> <span class="hljs-string">&quot;绿色&quot;</span>:<br>                        forceColor = Color.GREEN;<br>                        <span class="hljs-keyword">break</span>;<br>                    <span class="hljs-keyword">case</span> <span class="hljs-string">&quot;蓝色&quot;</span>:<br>                        forceColor = Color.BLUE;<br>                        <span class="hljs-keyword">break</span>;<br>                &#125;<br>            &#125;<br>        &#125;;<br><br>        <span class="hljs-comment">//为三个菜单项添加点击事件</span><br>        redItem.addActionListener(menuListener);<br>        greenItem.addActionListener(menuListener);<br>        blueItem.addActionListener(menuListener);<br>        <span class="hljs-comment">//把菜单项添加到右键菜单中</span><br>        colorMenu.add(redItem);<br>        colorMenu.add(greenItem);<br>        colorMenu.add(blueItem);<br>        <span class="hljs-comment">//把右键菜单添加到绘图区域drawArea</span><br>        drawArea.add(colorMenu);<br>        <span class="hljs-comment">//将iamge图片背景设置为白色</span><br>        g.fillRect(<span class="hljs-number">0</span>,<span class="hljs-number">0</span>,AREA_WIDTH,AREA_HEIGHT);<br>        <span class="hljs-comment">//设置绘图区域drawArea的大小</span><br>        drawArea.setPreferredSize(<span class="hljs-keyword">new</span> Dimension(AREA_WIDTH,AREA_HEIGHT));<br>        <span class="hljs-comment">//绘图区域drawArea设置鼠标移动监听器</span><br>        drawArea.addMouseMotionListener(<span class="hljs-keyword">new</span> MouseMotionAdapter() &#123;<br>            <span class="hljs-comment">//用于绘制图像</span><br>            <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">mouseDragged</span><span class="hljs-params">(MouseEvent e)</span> </span>&#123;<span class="hljs-comment">//按下鼠标键并拖动会触发</span><br>                <span class="hljs-comment">//如果上次鼠标的坐标在绘图区域，才开始绘图</span><br>                <span class="hljs-keyword">if</span> (preX&gt;<span class="hljs-number">0</span> &amp;&amp; preY&gt;<span class="hljs-number">0</span>)&#123;<br>                    <span class="hljs-comment">//设置当前选中的画笔颜色</span><br>                    g.setColor(forceColor);<br>                    <span class="hljs-comment">//绘制线条，需要有两组坐标，一组是上一次鼠标拖动鼠标时的坐标，一组是现在鼠标的坐标</span><br>                    g.drawLine(preX,preY,e.getX(),e.getY());<br>                &#125;<br><br>                <span class="hljs-comment">//更新preX和preY</span><br>                preX = e.getX();<br>                preY = e.getY();<br><br>                <span class="hljs-comment">//重新绘制drawArea组件</span><br>                drawArea.repaint();<br>            &#125;<br>        &#125;);<br>        drawArea.addMouseListener(<span class="hljs-keyword">new</span> MouseAdapter() &#123;<br><br>            <span class="hljs-comment">//用于弹出右键菜单</span><br>            <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">mouseReleased</span><span class="hljs-params">(MouseEvent e)</span> </span>&#123;<span class="hljs-comment">//松开鼠标键会触发</span><br>                <span class="hljs-keyword">boolean</span> popupTrigger = e.isPopupTrigger();<br>                <span class="hljs-keyword">if</span> (popupTrigger)&#123;<br>                    <span class="hljs-comment">//把colorMenu显示到drawArea画图区域，并跟随鼠标显示</span><br>                    colorMenu.show(drawArea,e.getX(),e.getY());<br>                &#125;<br>                <span class="hljs-comment">//当鼠标松开时，把preX和preY重置为-1</span><br>                preX = -<span class="hljs-number">1</span>;<br>                preY = -<span class="hljs-number">1</span>;<br><br>            &#125;<br>        &#125;);<br>        <span class="hljs-comment">//把drawArea添加到frame中</span><br>        frame.add(drawArea);<br><br>        <span class="hljs-comment">//设置frame最佳大小并可见</span><br>        frame.pack();<br>        frame.setVisible(<span class="hljs-keyword">true</span>);<br>    &#125;<br>    <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">main</span><span class="hljs-params">(String[] args)</span> </span>&#123;<br>        <span class="hljs-keyword">new</span> HandDraw().init();<br>    &#125;<br>&#125;<br></code></pre></td></tr></table></div></figure>



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              * @param {Number} end 结束索引
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}</script><script src="https://cdn.jsdelivr.net/npm/leancloud-storage@latest/dist/av-min.js"></script><script src="https://cdn.jsdelivr.net/npm/valine@latest/dist/Valine.min.js"></script><script>function loadValine () {
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